COMPOSITIONS OF BUPRENORPHINE AND µ ANTAGONISTS

ABSTRACT

The invention relates to a composition comprising buprenorphine and a μ opioid receptor antagonist, wherein the composition is characterized by an Agonist Antagonist Activity Index (AAnAI) of between about 0.7 and about 2.2; wherein;

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/576,233, filed on Dec. 15, 2011. The entire teachings of the aboveapplication are incorporated herein by reference.

BACKGROUND

The opioid neuropeptide system plays an important part in regulatingmood disorders. [Machado-Viera R. et. al.; Depression and Anxiety, 28(4) 2011, 267-281]. Opioid peptides and their receptors are potentialcandidates for the development of novel antidepressant treatment. Theactions of endogenous opioids and opiates are mediated by three receptortypes (μ, δ and κ), which are coupled to different intracellulareffector systems. [Berrocoso E. et. al., Current Pharmaceutical Design,15(14) 2009, 1612-22]. As such, agents that can modulate the actions ofone or more of the opioid receptor types with selectivity andsensitivity are important to treat the various diseases and disordersregulated by the opioid system.

The μ-opioid system has a profound effect on emotional state and ismodulated in the context of major depressive disorders (MDD) and changesin emotional state. The μ-opioid receptors are present and denselydistributed in brain regions implicated in the response to stressors andthe regulation and integration of emotionally significant stimuli. Theseinclude cortical regions, including the rostral anterior cingulate,prefrontal cortex [Eisenberger, Science 302, 2003, 290-2; Kennedy ArchGen Psychiatry 63(11), 2006, 1199-208; Zubieta, Science, 293 2001,311-5; Zubieta, Arch Gen Psychiatry, 60(11), 2003, 1145-53].Subcortically, the μ-opioid system is known to have a prominentregulatory role in the striatopallidal pathway (nucleus accumbens,ventral pallidum) and associated circuits (e.g., amygdala, thalamus,insular cortex) involved in the evaluation and response to salientstimuli, both rewarding and nonrewarding [Anderson A K, and Sobel N.Neuron 39(4) 2003, 581-3; Horvitz J C., Behav Neurosci. 114(5), 2000,934-9; Koob and Le Alcoholism Clinical & Experimental Research, 2001 25(5 Suppl.) 2001, 144S-151S; Napier and Mitrovic, Ann N Y Acad. Sci.,1999, 176-201; Price 2000; Quirarte, Brain Res., 808(2), 1998, 134-40.;Steiner and Gerfen, Exp Brain Res., 60-76, 1998; Zubieta, Science, 2932001, 311-5]. Activation of μ-opioid receptors increases dopamine whichmay contribute to anti-depressant effects including enhancement ofhedonic tone and sense of contentment, but will lead also to abuse whenthe increase in dopamine is higher than required to treat symptoms ofdepression.

Positron emission tomography (PET) studies in humans have shownfunctional effects of the μ-opioid system in the regulation of mood. Invivo μ-opioid receptor availability in the sub-amygdalar temporal cortexhas been found to inversely correlate with the metabolic responses ofthis region to the presentation of a negative emotional challenge[Liberzon, Proc Natl Acad. Sci. 99(10): 2002, 7084-9]. In a subsequentPET study emotional challenges were shown to elicit further differencesin brain g activity between normal human subjects, patients with SSRIresponsive MDD, and patients with treatment resistant depression[Kennedy, Curr. Psychiatry Rep. 8(6), 2006, 437-44].

It has been hypothesized that blockade of κ-receptor activation willhave a beneficial therapeutic effect in the treatment of depression. Thehypothesis is based on human and animal evidence generated primarilyduring the past two decades. The following discussion is adapted from arecent review by Knoll and Carlezon, Jr. [Brain Res. 2010, 56-73, 2010].Whereas μ-opioid receptor activation results in elevation of mood inhumans, activation of the κ-opioid receptor is associated with adverseeffects on mood, including dysphoria and anhedonia [Pfeiffer, Horm MetabRes., 18(12): 1986, 842-8].

Anatomically, the κ-opioid receptor and dynorphin, the primaryendogenous κ ligand, are expressed throughout limbic brain areasimplicated in the pathophysiology of depression. In addition todysphoria and anhedonia, some aspects of the aversive effects of κactivation appear to involve increased anxiety. κ-opioid receptors anddynorphin are expressed throughout brain areas involved in fear andanxiety, including the amygdala and extended amygdala (Alheid 2003;Fallon and Leslie 1986; Mansour, 1995b]. The effect of κ blockade inhumans has yet to be tested in humans; a pharmaceutically acceptableprobe has eluded medicinal chemistry efforts.

Treatment resistant depression (TRD), a widespread disease wherepatients with MDD do not achieve an adequate response to monoaminereuptake inhibitor anti-depressant therapy. Despite the emergence ofmultiple new therapeutic agents in recent decades, TRD remains a majorclinical and public health problem that results in significant adverseconsequences to patients, families, and society as a whole [Gibson, J.,Manag. Care, 16:370-377, 2010; Sackeim, Clin Psychiatry, 62 Suppl16:10-17, 2001]. Prior to the advent of monoamine oxidase inhibitors(MAOIs) and tricyclic antidepressants (TCAs), opioids were the primarytherapeutic modality for depression. Modern characterization of theendogenous opioid system has elaborated the role of opioidergic peptidesin the regulation of both stress response behaviors and hedonic tone.Buprenorphine, a partial μ-opioid agonist, has been reported to beuseful in treating depression in patients where other availabletherapies have failed. [Callaway, Soc. Biol. Psychiatry, 39, 1996,989-990; Emrich et. al., Neuropharmacology, 22, 1983, 385-388; Bodkinet. al., J. Clin. Psychopharmacology, 15, 49-57, 1995].

While opioid agonists have anti-depressant effects they are generallynot used to treat depression. Long-term use of a full μ-opioid agonistmay result in the development of opioid-dependency in patients. Inaddition there are other undesirable side effects including additivepotential, sedation, respiratory depression, nausea and constipationthat will accompany acute and chronic opioid use. Buprenorphine is anμ-opioid partial agonist which produces typical μ-opioid agonist effectsand side effects such as additive potential and respiratory depressionwhile producing maximal effects that are less than those of fullagonists like heroin and methadone. Buprenorphine produces sufficientμ-agonist effect to enable opioid-addicted individuals to discontinuethe misuse of opioids without experiencing withdrawal symptoms.

While there are many well-known opioid receptor binding compounds, thereis little evidence to guide the management of depression that has notresponded to a course of antidepressants. Treatment-refractorydepression is an important public health problem and large pragmatictrials are needed to inform clinical practice. [Stimpson et al. TheBritish Journal of Psychiatry, (2002) 181: 284-294]. There still remainsa need to develop effective treatments of mood disorders, in particularmajor depressive disorders.

SUMMARY OF THE INVENTION

The invention relates to a composition comprising buprenorphine and a μopioid receptor antagonist wherein the composition is characterized byan Agonist:Antagonist Activity Index (AAnAI) of between about 0.70 andabout 2.2; wherein;

${AAnAI} = \frac{\left\lbrack {C_{\max {({BUP})}}/{EC}_{50}} \right\rbrack}{\left\lbrack {C_{\max {({ANTAGONIST})}}/{IC}_{50}} \right\rbrack}$

-   -   wherein, EC₅₀ represents the half maximal effective serum        concentration of buprenorphine, expressed as nM;    -   IC₅₀ represents the half maximal inhibitory concentration of the        μ opioid antagonist in humans, expressed as nM;    -   C_(max(BUP)) represents the peak serum or plasma concentration        of buprenorphine and/or a μ opioid receptor agonist metabolite        of buprenorphine, expressed as nM; and    -   C_(max(ANTAGONIST)) represents the peak serum concentration of        the μ opioid antagonist and/or a μ opioid receptor antagonist        metabolite of said μ opioid antagonist, expressed as nM.

The invention further relates to the treatment of depression comprisingadministering a composition according to the invention to a subject inneed thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1: Efflux of dopamine in nucleus accumbens shell afteradministration of buprenorphine at 0.001 mg/kg, 0.01 mg/kg, 0.1 mg/kgand 1 mg/kg doses after subcutaneous (SC) administration.

FIG. 2: Average dopamine efflux following (SC) administration ofbuprenorphine at increasing doses.

FIG. 3: Reduction in the efflux of dopamine in nucleus accumbens shellfollowing administration of Compound-1, Compound-10, naltrexone andnalmefene with Buprenorphine (0.1 mg/kg).

FIG. 4: Log Activity Index (Log AAnAI) versus dopamine efflux forCompound-1, Compound-10, naltrexone and nalmefene with Buprenorphine(0.1 mg/kg).

FIG. 5: Increase in immobility following increased concentrations ofCompound-1 in forced swim test in WKY rats treated with Buprenorphine(0.1 mg/kg).

FIG. 6: The effect of Compound-1 on dopamine efflux in WKY ratsundergoing forced swim test after treatment with Buprenorphine (0.1mg/kg).

FIG. 7: The efflux of Compound-1 on 5-Hydroxyindoleacetic acid (5-HIAA)release in WKY rats undergoing the forced swim test after treatment withBuprenorphine (0.1 mg/kg).

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a composition comprising buprenorphine andanother opioid receptor binding compound, wherein the opioid receptorbinding compound is a μ opioid receptor antagonist, and the compositionhas an Agonist:Antagonist Activity Index (AAnAI) of between about 0.70and about 2.2; wherein;

${AAnAI} = \frac{\left\lbrack {C_{\max {({BUP})}}/{EC}_{50}} \right\rbrack}{\left\lbrack {C_{\max {({ANTAGONIST})}}/{IC}_{50}} \right\rbrack}$

-   -   wherein, EC₅₀ represents the half maximal effective serum        concentration of buprenorphine, expressed as nM;    -   IC₅₀ represents the half maximal inhibitory concentration of the        μ opioid antagonist in humans, expressed as nM;    -   C_(max(BUP)) represents the peak serum or plasma concentration        of buprenorphine and/or a μ opioid receptor agonist metabolite        of buprenorphine, expressed as nM; and    -   C_(max(ANTAGONIST)) represents the peak serum concentration of        the μ opioid antagonist and/or a μ opioid receptor antagonist        metabolite of said μ opioid antagonist, expressed as nM.

Buprenorphine (BUP) was studied in combination with varying amounts ofan opioid antagonist, Compound-1. This study utilized two ratios of theμ opioid receptor antagonist Compound-1 and buprenorphine, with theratios defined by the amount of each drug (in mg) administered: a) 1:8and b) 1:1 to evaluate safety and tolerability in patients. The 1:8(Compound1-BUP) did show an anti-depressive effect however that changefrom placebo was not statistically significant. The 1:1 ratio not onlyproved to be better tolerated, but unexpectedly also provided a clearimprovement (statistically significant and clinically meaningful versusplacebo) in depression over the duration of this trial. While notwanting to be held to any particular theory, it had been thought that atthe lower ratio (1:8) greater μ agonist activity would yield greaterimprovement in anti-depressive effects. It was an unexpected findingthat less μ activity as exemplified by the higher ratio (1:1), was notonly adequate to exert an anti-depressive effect, but the effects weregreater than that observed with the 1:8 ratio. While the ratios abovewere based on mass of drug delivered, when the molecular pharmacology,systemic concentrations achieved (a function of bioavailability by theintended route and clearance) and the relative degree ofagonist:antagonist activity was evaluated it was clear that a net opioidagonist activity was present at both the 1:8 and 1:1 ratios. Thisapproach allowed for the determination of the preferred degree ofbalance between agonist and antagonist activity for the manifestation ofan anti-depressive while eliminating the undesired effects, for example,the high associated with the addictive potential of opioids. The 1:8ratio of Compound-1:BUP did not result in a statistical or clinicallymeaningful improvement in depression, and at this ratio patients stillreported a “high” and sedation; the calculated “agonist:antagonistactivity index” (AAnAI) was 13.4. In contrast, for the 1:1 ratio theAAnAI was 1.3. As used herein, the term “addictive potential” refers tothe current Diagnostic and Statistical Manual of Mental Disorders(DSM-IV) definition for substance dependence, defined as: the abilityfor a compound or substance to illicit physiological dependence,evidence of tolerance or withdrawal. Without being bound to anyparticular theory, it is believed that to achieve the desiredanti-depressive effect the preferred AAnAI is between the values ofabout 0.5 and 5.0, preferably about 0.7 and about 2.2. In oneembodiment, the AAnAI is between about 0.6 and 4.0. In one embodiment,the AAnAI is between about 0.7 and 3.0. In a preferred embodiment, theAAnAI is between about 0.8 and about 2.1, preferably between about 1.0and about 2.0, preferably between about 1.0 and about 1.8, preferablybetween about 1.1 and about 1.6, preferably between about 1.2 and about1.4, most preferably about 1.3.

An AAnAI can be determined for buprenorphine and any compoundcharacterized as a μ receptor antagonist. The following information isrequired for the μ receptor antagonist: 1) IC₅₀ based on GTPγS assay;and 2) C_(max) concentration following dosing. For buprenorphine thefollowing are required: 1) EC₅₀ based on GTPγS assay; and 2) C_(max)concentrations following dosing. Other functional assays could also beused based on cAMP or other downstream end-points following receptoractivation; however the GTPγS is the preferred approach. The doseyielding a C_(max) value for buprenorphine or the μ opioid receptorantagonist may vary with the route of administration. Since the AAnAI isbased on C_(max) it can be calculated for any route of administrationfor the combination. Thus AAnAI is the ratio between the activities ofbuprenorphine and a μ receptor antagonist as shown below:

${AAnAI} = \frac{\left\lbrack {C_{\max {({BUP})}}/{EC}_{50}} \right\rbrack}{\left\lbrack {C_{\max {({ANTAGONIST})}}/{IC}_{50}} \right\rbrack}$

The EC₅₀ and IC₅₀ values for buprenorphine (BUP) and Compound-1 areshown in Table-1 below. These values were determined using the GTPγSfunctional assay.

TABLE 1 Buprenorphine Compound-1 EC₅₀ (nM) Emax IC₅₀ (nM) Imax 0.11 32%0.9 >95%

Plasma concentrations of buprenorphine and Compound-1 were determined inpatients following the different dosing paradigms. (Table 2) The C_(max)values are reported below for each drug. C_(max) values are typicallyreported as mass/mL. These parameters reflect the potency of thebuprenorphine and the μ opioid receptor antagonist.

TABLE 2 Dose Observed C_(max)/IC or AAnA Drug (mg) C_(max) (ng/mL) nM atC_(max) EC₅₀ Index Compound-1 0.5 1.4 3.8 4.4 13.4 BUP 4 3.0 6.4 58.3Compound-1 8 25.8 69.6 79.1 1.3 BUP 8 5.2 11.1 101.1

Compound-1 C_(max) ranges from 3.7 to 77× its IC₅₀ value for inhibitingthe μ opioid receptor, while the buprenorphine C_(max) ranges from about57-99× its EC₅₀ as a partial agonist. At the lower ratio (1:8) thepartial μ agonist activity would dominate. While at the higher ratio(1:1) the μ signaling would be greatly diminished. This agrees well withthe observed clinical data. It also establishes the desired ratio thatwould be required for any μ antagonist in combination with BUP to treatdepression while eliminating “high” and development of dependency. Thedesired range for this ratio, defined here as the AAnAI, would be about0.5 to about 5 for any drug displaying antagonist activity at the μreceptor, including Compound-1, naltrexone and nalmefene. At theseratios μ signaling adequate to exert an anti-depressive effect, withoutthe patient experiencing signs of being associated with the addictivepotential of opioids, in particular buprenorphine.

The AAnAI can be calculated for any μ opioid antagonist. Naltrexone andnalmefene are two common μ opioid antagonists. In the example below, theAAnAI for naltrexone is shown for a range of C_(max) values based on adose of buprenorphine of 8 mg. Since the functional IC₅₀ value is 4.8 nMfor naltrexone, higher C_(max) values are required to achieve the sameAAnAI as with Compound-1. (Table 3) Estimated dose range of naltrexonewould be between 350 and 1050 mg to cover ratios of the “BUPagonist:antagonist activity” ratio of between 1 and 2.

TABLE 3 Drug C_(max) (ng/ml) C_(max) (nM) C_(max)/IC₅₀ AAnAI naltrexone10 29 6.1 16.6 50 146 30.5 3.3 100 293 61.0 1.7 150 439 91.5 1.1 200 586122 0.8

In addition to differences in potency of antagonists, the ADME(Absorption, Distribution, Metabolism and Excretion) properties of thecompound illustrate why a simple ratio based on the administered dosecannot be used to predict the ability of the combination ofbuprenorphine and an opioid antagonist to treat depression. Again usingnaltrexone as the example, plasma concentrations achieved with a 50 mgdose of naltrexone are illustrated. The C_(max) for naltrexone isapproximately 10 ng/mL. Naltrexone displays fairly dose-proportionalpharmacokinetics. Consequently, the oral dose of naltrexone needed toachieve the desired AAnAI would be between about 350 and 750 mg.Importantly, to achieve the same AAnAI shown to have a clear clinicalbenefit for the buprenorphine-Compound-1 combination, the dose ofnaltrexone required would be about 625 mg and the simple ratio based onoral dose would be almost 80:1.

Similar calculations can be made for nalmefene (Table 4) based onpublished literature values for the IC₅₀ (13 nM) and reported plasmaconcentrations following oral administration. Based on the availableliterature to achieve the desired AAnAI, plasma concentrations of about210 to 400 ng/mL are required.

TABLE 4 Drug C_(max) (ng/ml) C_(max) (nM) C_(max)/IC₅₀ AAnAI Nalmefene25 74 5.7 17.8 100 295 22.7 4.5 200 589 45.3 2.2 300 884 68.0 1.5 4001178 90.7 1.1 500 1473 113.3 0.9

The IC₅₀ for nalmefene was determined using the methods described hereinand found to be more potent than previously described in the literature.The AAnAI values based on an IC₅₀ of 2.2 nM are provided below in Table4A.

TABLE 4A Drug C_(max) (ng/ml) C_(max) (nM) C_(max)/IC₅₀ AAnAI Nalmefene6.25 18.5 8.4 12.0 12.5 37 16.8 6.0 25 74 33.6 3.0 100 295 134 0.75 200589 267 0.38

In some embodiments, the administration of an antagonist resulting in anAAnAI of between about 0.5 to about 5.0, preferably between about 0.7 to2.2, modulates dopamine release. In one embodiment, the administrationof a combination of buprenorphine and an antagonist of the inventionresults in a decrease in the production of dopamine in the nucleusaccumbens shell in comparison with administration of buprenorphinealone. In a preferred embodiment, the administration of a combination ofbuprenorphine and Compound-1 having an activity index of between about0.7 and about 2.2 results in a reduction in the dopamine releasecompared to the administration of buprenorphine alone. In a preferredembodiment, the combination of buprenorphine and an antagonist of theinvention results in an average dopamine level of between about 1pg/sample to about 2 pg/sample whereas the administration ofbuprenorphine alone (0.1 mg/kg) results in about 3 pg/sample after 2hours. In one embodiment, the combination of buprenorphine and anantagonist of the invention, having an AAnAI of between about 0.7 toabout 2.2, results in a reduction in dopamine release of between about25% to about 75% in comparison with the administration of buprenorphinealone in a stimulated dopamine efflux test. Without being bound to anyparticular theory, the reduction in dopamine release is postulated to beuseful in reducing the drug liking and addictive potential ofbuprenorphine, while retaining properties that contribute to ananti-depressive effect. Importantly, attenuation of μ-opioid signalingfurther by achieving an AAnAI of less than 0.5 would be undesirable witha loss of anti-depressive effect.

In a preferred embodiment, the μ opioid receptor antagonist is acompound of Formula I:

or a pharmaceutically acceptable salt, ester or prodrug thereof wherein;s is 0, 1 or 2;t is 0, 1, 2, 3, 4, 5, 6, or 7;

X is S or O;

R₁ is selected from aliphatic, substituted aliphatic, aryl, substitutedaryl, heterocyclyl or substituted heterocyclyl;each R₂, R₃, R₄, R₅, R₆, R₇ and R₈ is independently selected fromabsent, hydrogen, halogen, —OR₂₀, —SR₂₀, —NR₂₀R₂₁, —C(O)R₂₀, —C(O)OR₂₀,—C(O)NR₂₀R₂₁, —N(R₂₀)C(O)R₂₁, —CF₃, —CN, —NO₂, —N₃, acyl, alkoxy,substituted alkoxy, alkylamino, substituted alkylamino, dialkylamino,substituted dialkylamino, substituted or unsubstituted alkylthio,substituted or unsubstituted alkylsulfonyl, optionally substitutedaliphatic, optionally substituted aryl, heterocyclyl or substitutedheterocyclyl;each R₉ and R₁₀ is selected from hydrogen, aliphatic, substitutedaliphatic, aryl, substituted aryl, heterocyclyl or substitutedheterocyclyl;alternatively, two of R₂, R₃, R₄, R₅, R₆, R₇ and R₈ together with theatoms they are attached to form an optionally substituted ring;alternatively R₂ and R₃ together with the carbon they are attached toform a C═X group;wherein each R₂₀ and R₂₁ is independently selected from absent,hydrogen, halogen, —OH, —SH, —NH₂, —CF₃, —CN, —NO₂, —N₃, —C(O)OH,—C(O)NH₂, acyl, alkoxy, substituted alkoxy, alkylamino, substitutedalkylamino, dialkylamino, substituted dialkylamino, substituted orunsubstituted alkylthio, substituted or unsubstituted alkylsulfonyl,aliphatic, substituted aliphatic, aryl or substituted aryl; andalternatively R₉ and R₁₀ together with the atom they are attached toform an optionally substituted ring; alternatively two R₅ groups, or anR₅ and an R₆ group, together with the carbon they are attached to form aC═X group.

In a more preferred embodiment, the μ receptor antagonist is a compoundof Formula II:

or a pharmaceutically acceptable salt, ester or prodrug thereof wherein;

X is S or O;

R₁ is —(CH₂)_(n)-c-C₃H₅, —(CH₂)_(n)-c-C₄H₇, —(CH₂)_(n)-c-C₅H₉,—(CH₂)_(n)—CH═CH₂ or —(CH₂)_(n)—CH═C(CH₃)₂ wherein n and m areindependently 0, 1, 2 or 3;R₆ and R₇ are independently H, —OH or together R₆ and R₇ form an —O— or—S— group; andR₅ and R₁₁ are independently H, —OH, OCH₃ or together R₅ and R₁ form a═O or ═CH₂ group.In a more preferred embodiment, the μ receptor antagonist is selectedfrom:

The invention further relates to the treatment of a depressive disordercomprising administering a composition according to the invention to asubject in need thereof. In a preferred embodiment, the depressivedisorder is selected from major depressive disorder, chronic depression,severe unipolar recurrent major depressive episodes, dysthymic disorder,depressive neurosis and neurotic depression, melancholic depression,atypical depression, reactive depression, treatment resistantdepression, seasonal affective disorder and pediatric depression;premenstrual syndrome, premenstrual dysphoric disorder, hot flashes,bipolar disorders or manic depression, bipolar I disorder, bipolar IIdisorder and cyclothymic disorder. In a preferred embodiment, thedepressive disorder is a major depressive disorder. In a more preferredembodiment, the depressive disorder is treatment resistant depression.

The invention further relates to the treatment of obsessive compulsivedisorder, bulimia nervosa, panic disorder, posttraumatic stress disorder(PTSD), premenstrual dysphoric disorder (PMDD), social anxiety disorderand generalized anxiety disorder (GAD).

DEFINITIONS

Listed below are definitions of various terms used to describe thisinvention. These definitions apply to the terms as they are usedthroughout this specification and claims, unless otherwise limited inspecific instances, either individually or as part of a larger group.

The term “aliphatic group” or “aliphatic” refers to a non-aromaticmoiety that may be saturated (e.g. single bond) or contain one or moreunits of unsaturation, e.g., double and/or triple bonds. An aliphaticgroup may be straight chained, branched or cyclic, contain carbon,hydrogen or, optionally, one or more heteroatoms and may be substitutedor unsubstituted. In addition to aliphatic hydrocarbon groups, aliphaticgroups include, for example, polyalkoxyalkyls, such as polyalkyleneglycols, polyamines, and polyimines, for example. Such aliphatic groupsmay be further substituted. It is understood that aliphatic groups mayinclude alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl,substituted alkynyl, and substituted or unsubstituted cycloalkyl groupsas described herein.

The term “acyl” refers to a carbonyl substituted with hydrogen, alkyl,partially saturated or fully saturated cycloalkyl, partially saturatedor fully saturated heterocycle, aryl, or heteroaryl. For example, acylincludes groups such as (C₁-C₆) alkanoyl (e.g., formyl, acetyl,propionyl, butyryl, valeryl, caproyl, t-butylacetyl, etc.),(C₃-C₆)cycloalkylcarbonyl (e.g., cyclopropylcarbonyl,cyclobutylcarbonyl, cyclopentylcarbonyl, cyclohexylcarbonyl, etc.),heterocyclic carbonyl (e.g., pyrrolidinylcarbonyl,pyrrolid-2-one-5-carbonyl, piperidinylcarbonyl, piperazinylcarbonyl,tetrahydrofuranylcarbonyl, etc.), aroyl (e.g., benzoyl) and heteroaroyl(e.g., thiophenyl-2-carbonyl, thiophenyl-3-carbonyl, furanyl-2-carbonyl,furanyl-3-carbonyl, 1H-pyrroyl-2-carbonyl, 1H-pyrroyl-3-carbonyl,benzo[b]thiophenyl-2-carbonyl, etc.). In addition, the alkyl,cycloalkyl, heterocycle, aryl and heteroaryl portion of the acyl groupmay be any one of the groups described in the respective definitions.When indicated as being “optionally substituted”, the acyl group may beunsubstituted or optionally substituted with one or more substituents(typically, one to three substituents) independently selected from thegroup of substituents listed below in the definition for “substituted”or the alkyl, cycloalkyl, heterocycle, aryl and heteroaryl portion ofthe acyl group may be substituted as described above in the preferredand more preferred list of substituents, respectively.

The term “alkyl” is intended to include both branched and straightchain, substituted or unsubstituted saturated aliphatic hydrocarbonradicals/groups having the specified number of carbons. Preferred alkylgroups comprise about 1 to about 24 carbon atoms (“C₁-C₂₄”). Otherpreferred alkyl groups comprise at about 1 to about 8 carbon atoms(“C₁-C₈”) such as about 1 to about 6 carbon atoms (“C₁-C₆”), or such asabout 1 to about 3 carbon atoms (“C₁-C₃”). Examples of C₁-C₆ alkylradicals include, but are not limited to, methyl, ethyl, propyl,isopropyl, n-butyl, tert-butyl, n-pentyl, neopentyl and n-hexylradicals.

The term “alkenyl” refers to linear or branched radicals having at leastone carbon-carbon double bond. Such radicals preferably contain fromabout two to about twenty-four carbon atoms (“C₂-C₂₄”). Other preferredalkenyl radicals are “lower alkenyl” radicals having two to about tencarbon atoms (“C₂-C₁₀”) such as ethenyl, allyl, propenyl, butenyl and4-methylbutenyl. Preferred lower alkenyl radicals include 2 to about 6carbon atoms (“C₂-C₆”). The terms “alkenyl”, and “lower alkenyl”,embrace radicals having “cis” and “trans” orientations, oralternatively, “E” and “Z” orientations.

The term “alkynyl” refers to linear or branched radicals having at leastone carbon-carbon triple bond. Such radicals preferably contain fromabout two to about twenty-four carbon atoms (“C₂-C₂₄”). Other preferredalkynyl radicals are “lower alkynyl” radicals having two to about tencarbon atoms such as propargyl, 1-propynyl, 2-propynyl, 1-butyne,2-butynyl and 1-pentynyl. Preferred lower alkynyl radicals include 2 toabout 6 carbon atoms (“C₂-C₆”).

The term “cycloalkyl” refers to saturated carbocyclic radicals havingthree to about twelve carbon atoms (“C₃-C₁₂”). The term “cycloalkyl”embraces saturated carbocyclic radicals having three to about twelvecarbon atoms. Examples of such radicals include cyclopropyl, cyclobutyl,cyclopentyl and cyclohexyl.

The term “cycloalkenyl” refers to partially unsaturated carbocyclicradicals having three to twelve carbon atoms. Cycloalkenyl radicals thatare partially unsaturated carbocyclic radicals that contain two doublebonds (that may or may not be conjugated) can be called“cycloalkyldienyl”. More preferred cycloalkenyl radicals are “lowercycloalkenyl” radicals having four to about eight carbon atoms. Examplesof such radicals include cyclobutenyl, cyclopentenyl and cyclohexenyl.

The term “alkylene,” as used herein, refers to a divalent group derivedfrom a straight chain or branched saturated hydrocarbon chain having thespecified number of carbons atoms. Examples of alkylene groups include,but are not limited to, ethylene, propylene, butylene,3-methyl-pentylene, and 5-ethyl-hexylene.

The term “alkenylene,” as used herein, denotes a divalent group derivedfrom a straight chain or branched hydrocarbon moiety containing thespecified number of carbon atoms having at least one carbon-carbondouble bond. Alkenylene groups include, but are not limited to, forexample, ethenylene, 2-propenylene, 2-butenylene,1-methyl-2-buten-1-ylene, and the like.

The term “alkynylene,” as used herein, denotes a divalent group derivedfrom a straight chain or branched hydrocarbon moiety containing thespecified number of carbon atoms having at least one carbon-carbontriple bond. Representative alkynylene groups include, but are notlimited to, for example, propynylene, 1-butynylene,2-methyl-3-hexynylene, and the like.

The term “alkoxy” refers to linear or branched oxy-containing radicalseach having alkyl portions of one to about twenty-four carbon atoms or,preferably, one to about twelve carbon atoms. More preferred alkoxyradicals are “lower alkoxy” radicals having one to about ten carbonatoms and more preferably having one to about eight carbon atoms.Examples of such radicals include methoxy, ethoxy, propoxy, butoxy andtert-butoxy.

The term “alkoxyalkyl” refers to alkyl radicals having one or morealkoxy radicals attached to the alkyl radical, that is, to formmonoalkoxyalkyl and dialkoxyalkyl radicals.

The term “aryl”, alone or in combination, means an aromatic systemcontaining one, two or three rings wherein such rings may be attachedtogether in a pendent manner or may be fused. The term “aryl” embracesaromatic radicals such as phenyl, naphthyl, tetrahydronaphthyl, indanefuranyl, quinazolinyl, pyridyl and biphenyl.

The terms “heterocyclyl”, “heterocycle” “heterocyclic” or “heterocyclo”refer to saturated, partially unsaturated and unsaturatedheteroatom-containing ring-shaped radicals, which can also be called“heterocyclyl”, “heterocycloalkenyl” and “heteroaryl” correspondingly,where the heteroatoms may be selected from nitrogen, sulfur and oxygen.Examples of saturated heterocyclyl radicals include saturated 3 to6-membered heteromonocyclic group containing 1 to 4 nitrogen atoms (e.g.pyrrolidinyl, imidazolidinyl, piperidino, piperazinyl, etc.); saturated3 to 6-membered heteromonocyclic group containing 1 to 2 oxygen atomsand 1 to 3 nitrogen atoms (e.g. morpholinyl, etc.); saturated 3 to6-membered heteromonocyclic group containing 1 to 2 sulfur atoms and 1to 3 nitrogen atoms (e.g., thiazolidinyl, etc.). Examples of partiallyunsaturated heterocyclyl radicals include dihydrothiophene,dihydropyran, dihydrofuran and dihydrothiazole. Heterocyclyl radicalsmay include a pentavalent nitrogen, such as in tetrazolium andpyridinium radicals. The term “heterocycle” also embraces radicals whereheterocyclyl radicals are fused with aryl or cycloalkyl radicals.Examples of such fused bicyclic radicals include benzofuran,benzothiophene, and the like.

The term “heteroaryl” refers to unsaturated aromatic heterocyclylradicals. Examples of heteroaryl radicals include unsaturated 3 to 6membered heteromonocyclic group containing 1 to 4 nitrogen atoms, forexample, pyrrolyl, pyrrolinyl, imidazolyl, pyrazolyl, pyridyl,pyrimidyl, pyrazinyl, pyridazinyl, triazolyl (e.g., 4H-1,2,4-triazolyl,1H-1,2,3-triazolyl, 2H-1,2,3-triazolyl, etc.) tetrazolyl (e.g.1H-tetrazolyl, 2H-tetrazolyl, etc.), etc.; unsaturated condensedheterocyclyl group containing 1 to 5 nitrogen atoms, for example,indolyl, isoindolyl, indolizinyl, benzimidazolyl, quinolyl, isoquinolyl,indazolyl, benzotriazolyl, tetrazolopyridazinyl (e.g.,tetrazolo[1,5-b]pyridazinyl, etc.), etc.; unsaturated 3 to 6-memberedheteromonocyclic group containing an oxygen atom, for example, pyranyl,furyl, etc.; unsaturated 3 to 6-membered heteromonocyclic groupcontaining a sulfur atom, for example, thienyl, etc.; unsaturated 3- to6-membered heteromonocyclic group containing 1 to 2 oxygen atoms and 1to 3 nitrogen atoms, for example, oxazolyl, isoxazolyl, oxadiazolyl(e.g., 1,2,4-oxadiazolyl, 1,3,4-oxadiazolyl, 1,2,5-oxadiazolyl, etc.)etc.; unsaturated condensed heterocyclyl group containing 1 to 2 oxygenatoms and 1 to 3 nitrogen atoms (e.g. benzoxazolyl, benzoxadiazolyl,etc.); unsaturated 3 to 6-membered heteromonocyclic group containing 1to 2 sulfur atoms and 1 to 3 nitrogen atoms, for example, thiazolyl,thiadiazolyl (e.g., 1,2,4-thiadiazolyl, 1,3,4-thiadiazolyl,1,2,5-thiadiazolyl, etc.) etc.; unsaturated condensed heterocyclyl groupcontaining 1 to 2 sulfur atoms and 1 to 3 nitrogen atoms (e.g.,benzothiazolyl, benzothiadiazolyl, etc.) and the like.

The term “heterocycloalkyl” refers to heterocyclo-substituted alkylradicals. More preferred heterocycloalkyl radicals are “lowerheterocycloalkyl” radicals having one to six carbon atoms in theheterocyclo radical.

The term “alkylthio” refers to radicals containing a linear or branchedalkyl radical, of one to about ten carbon atoms attached to a divalentsulfur atom. Preferred alkylthio radicals have alkyl radicals of one toabout twenty-four carbon atoms or, preferably, one to about twelvecarbon atoms. More preferred alkylthio radicals have alkyl radicalswhich are “lower alkylthio” radicals having one to about ten carbonatoms. Most preferred are alkylthio radicals having lower alkyl radicalsof one to about eight carbon atoms. Examples of such lower alkylthioradicals include methylthio, ethylthio, propylthio, butylthio andhexylthio.

The terms “aralkyl” or “arylalkyl” refer to aryl-substituted alkylradicals such as benzyl, diphenylmethyl, triphenylmethyl, phenylethyl,and diphenylethyl.

The term “aryloxy” refers to aryl radicals attached through an oxygenatom to other radicals.

The terms “aralkoxy” or “arylalkoxy” refer to aralkyl radicals attachedthrough an oxygen atom to other radicals.

The term “aminoalkyl” refers to alkyl radicals substituted with aminoradicals. Preferred aminoalkyl radicals have alkyl radicals having aboutone to about twenty-four carbon atoms or, preferably, one to abouttwelve carbon atoms. More preferred aminoalkyl radicals are “loweraminoalkyl” that have alkyl radicals having one to about ten carbonatoms. Most preferred are aminoalkyl radicals having lower alkylradicals having one to eight carbon atoms. Examples of such radicalsinclude aminomethyl, aminoethyl, and the like.

The term “alkylamino” denotes amino groups which are substituted withone or two alkyl radicals. Preferred alkylamino radicals have alkylradicals having about one to about twenty carbon atoms or, preferably,one to about twelve carbon atoms. More preferred alkylamino radicals are“lower alkylamino” that have alkyl radicals having one to about tencarbon atoms. Most preferred are alkylamino radicals having lower alkylradicals having one to about eight carbon atoms. Suitable loweralkylamino may be monosubstituted N-alkylamino or disubstitutedN,N-alkylamino, such as N-methylamino, N-ethylamino, N,N-dimethylamino,N,N-diethylamino or the like.

The term “substituted” refers to the replacement of one or more hydrogenradicals in a given structure with the radical of a specifiedsubstituent including, but not limited to: halo, alkyl, alkenyl,alkynyl, aryl, heterocyclyl, thiol, alkylthio, arylthio, alkylthioalkyl,arylthioalkyl, alkylsulfonyl, alkylsulfonylalkyl, arylsulfonylalkyl,alkoxy, aryloxy, aralkoxy, aminocarbonyl, alkylaminocarbonyl,arylaminocarbonyl, alkoxycarbonyl, aryloxycarbonyl, haloalkyl, amino,trifluoromethyl, cyano, nitro, alkylamino, arylamino, alkylaminoalkyl,arylaminoalkyl, aminoalkylamino, hydroxy, alkoxyalkyl, carboxyalkyl,alkoxycarbonylalkyl, aminocarbonylalkyl, acyl, aralkoxycarbonyl,carboxylic acid, sulfonic acid, sulfonyl, phosphonic acid, aryl,heteroaryl, heterocyclic, and aliphatic. It is understood that thesubstituent may be further substituted.

For simplicity, chemical moieties that are defined and referred tothroughout can be univalent chemical moieties (e.g., alkyl, aryl, etc.)or multivalent moieties under the appropriate structural circumstancesclear to those skilled in the art. For example, an “alkyl” moiety can bereferred to a monovalent radical (e.g. CH₃—CH₂—), or in other instances,a bivalent linking moiety can be “alkyl,” in which case those skilled inthe art will understand the alkyl to be a divalent radical (e.g.,—CH₂—CH₂—), which is equivalent to the term “alkylene.” Similarly, incircumstances in which divalent moieties are required and are stated asbeing “alkoxy”, “alkylamino”, “aryloxy”, “alkylthio”, ‘aryl”,“heteroaryl”, “heterocyclic”, “alkyl” “alkenyl”, “alkynyl”, “aliphatic”,or “cycloalkyl”, those skilled in the art will understand that the termsalkoxy”, “alkylamino”, “aryloxy”, “alkylthio”, “aryl”, “heteroaryl”,“heterocyclic”, “alkyl”, “alkenyl”, “alkynyl”, “aliphatic”, or“cycloalkyl” refer to the corresponding divalent moiety.

The terms “halogen” or “halo” as used herein, refers to an atom selectedfrom fluorine, chlorine, bromine and iodine.

The terms “compound” “drug”, and “prodrug” as used herein all includepharmaceutically acceptable salts, co-crystals, solvates, hydrates,polymorphs, enantiomers, diastereoisomers, racemates and the like of thecompounds, drugs and prodrugs having the formulas as set forth herein.

Substituents indicated as attached through variable points ofattachments can be attached to any available position on the ringstructure.

As used herein, the term “effective amount of the subject compounds,”with respect to the subject method of treatment, refers to an amount ofthe subject compound which, when delivered as part of desired doseregimen, brings about management of the disease or disorder toclinically acceptable standards.

“Treatment” or “treating” refers to an approach for obtaining beneficialor desired clinical results in a patient. For purposes of thisinvention, beneficial or desired clinical results include, but are notlimited to, one or more of the following: alleviation of symptoms,diminishment of extent of a disease, stabilization (i.e., not worsening)of a state of disease, preventing occurrence or recurrence of disease,delay or slowing of disease progression, amelioration of the diseasestate, and remission (whether partial or total).

As used herein, the term “major depressive disorder” (MDD) is used asthat term is understood in art, and refers to a diagnosis that is guidedby diagnostic criteria listed in Diagnostic and Statistical Manual ofMental Disorders, Fourth Edition (DSM-IV) or ICD-10, or in similarnomenclatures.

Patients suffering from “treatment resistant depression” include (1)those who fail to respond to standard doses (i.e., significantlysuperior to placebo in double-blind studies) of antidepressants (such asa monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants(TCAs), tetracyclic antidepressants (TeCAs), selective serotoninreuptake inhibitors (SSRIs), and serotonin-norepinephrine reuptakeinhibitors (SNRIs)) administered continuously for a minimum duration of6 weeks, and (2) those who fail to respond to standard doses of anantidepressant (such as a monoamine oxidase inhibitors (MAOIs),tricyclic antidepressants (TCAs), tetracyclic antidepressants (TeCAs),selective serotonin reuptake inhibitors (SSRIs), andserotonin-norepinephrine reuptake inhibitors (SNRIs)) (monotherapy)administered continuously for a minimum duration of 12 weeks. Onecriteria for determining whether a patient's depression is treatmentresistant to an antidepressant is if a Clinical GlobalImpression-Improvement (CGI-I) score of 1 (very much improved) or 2(much improved) is not achieved by the end of a 6, 8, or 12 week trial.The CGI-I scale is defined in Guy, W. (ed.): ECDEU Assessment Manual forPsychopharmacology, Revised, DHEW Pub. No. (ADM) 76-338, Rockville, Md.,National Institute of Mental Health, 1976.

EXAMPLES Example 1

A randomized, double-blind, placebo-controlled study was conductedevaluating the safety and tolerability of a combination of buprenorphinewith Compound-1. The study was conducted in 32 adults with majordepressive disorder who had an inadequate response to antidepressanttherapy. In this study, subjects received a once daily sublingual doseof placebo or Compound-1-BUP at dose ratios of 1:8 or 1:1 withcorresponding escalating doses of 0.25:2 mg/0.5:4 mg and 4:4 mg/8:8 mg,respectively, for 7 days.

Among the most common adverse events were dizziness, nausea, vomiting,and sedation (all of which were reported more frequently by subjects inthe 1:8 ratio group (Cohort A) versus subjects in the 1:1 ratio (CohortB) or placebo groups). For example, while about 28.5% of Cohort Areported sedation or somnolence, only 7% of Cohort B reported sedationor somnolence. The occurrence of dizziness was also significantly higherin Cohort A (57%) compared to Cohort B (29%). A summary of the mostcommon adverse events (i.e, those reported by ≧10% of subjects in anytreatment group) is provided in Table A:

TABLE A Comparison of most common adverse events (>10% in any group)between placebo, Cohort A and Cohort B Adverse Event Preferred TermPlacebo Cohort A Cohort B (N, %) (N = 4) (N = 14) (N = 14) Dizziness 08(57) 4(29) Nausea 1(25) 4(29) 3(21) Vomiting 0 4(29)* 2(14)*Hyperhidrosis 1(25) 2(14) 0 Menorrhagia 1(25) 0 0 Pain in extremity1(25) 0 1(7) Constipation 0 2(14) 3(21) Sedation or 0 4(28.5) 1(7)somnolence Fatigue 0 2(14) 1(7) Feeling abnormal 0 0 2(14) Flushing 02(14) 0 *One subject from each active group discontinued due tovomiting. Cohort A: 1:8 ratio of Compound 1: Buprenorphine (0.25 mg:2 mgfor days 1 to 3 and 0.5 mg:4 mg for days 4 to 7) Cohort B: 1:1 ratio ofCompound 1: Buprenorphine (4 mg:4 mg for days 1 to 3 and 8 mg:8 mg fordays 4 to 7

Efficacy was measured by changes from baseline to Day 7 in the 17-itemHamilton Rating Scale for Depression (HAM-D-17) and theMontgomery-Åsberg Depression Rating Scale (MADRS). For subjects treatedwith Compound-1-BUP at the 1:8 and 1:1 dose ratios or placebo, mean(standard deviation) changes from baseline to day 7 in HAM-D-17 totalscores were −5.0 (6.1), −6.7 (3.4), and −1.0 (4.2), respectively(p=0.032 for the 1:1 ratio versus placebo) and mean (SD) changes frombaseline to day 7 in MADRS total scores were −8.5 (0.4), −11.4 (6.6),and −3.5 (5.8), respectively. See Tables B and C.

TABLE B Comparison of treatment efficacy between placebo, Cohort A andCohort B assessed by Hamilton Depression Rating Sacle-17 (Total Score)Placebo Cohort A Cohort B Parameter (PBO) (1:8) (1:1) Baseline score #subjects N = 4 N = 14 N = 14 mean (SD) 19.0 (3.2) 17.5 (2.0) 19.4 (2.7)median 18.5 17.5 19.0 Change from # subjects N = 4 N = 13 N = 13baseline at Day 7 mean (SD) −1.0 (4.2) −5.0 (6.1) −6.7 (3.4) median 0−4.0 −6.0 Comparison of Cohort A vs. Cohort B vs. changes from PBO PBObaseline mean (SD)  −4 (5.78) −5.69 (3.57) P value* 0.337 0.032 *p valuefrom exact Wilcoxon test Cohort A: 1:8 ratio of Compound 1:Buprenorphine (0.25 mg:2 mg for days 1 to 3 and 0.5 mg:4 mg for days 4to 7) Cohort B: 1:1 ratio of Compound 1: Buprenorphine (4 mg:4 mg fordays 1 to 3 and 8 mg:8 mg for days 4 to 7

TABLE C Comparison of treatment efficacy between placebo, Cohort A andCohort B assessed by Montgomery-Åsberg Depression Rating Scale (TotalScore) Cohort A Cohort B Parameter Placebo (1:8) (1:1) Baseline score #subjects N = 4 N = 14 N = 14 mean (SD) 24.5 (7.9) 23.3 (4.1) 26.4 (4.4)Median 26.0 23.5 26.0 Change from # subjects N = 4 N = 13 N = 13baseline at Day 7 mean (SD) −3.5 (5.8) −8.5 (7.4) −11.4 (6.6)  median−2.5 −9.0 −13.0 Comparison of Cohort A vs. Cohort B vs. changes from PBOPBO baseline mean (SD) −4.96 (7.10) −7.88 (6.41) P value* 0.256 0.054Cohort A: 1:8 ratio of Compound 1: Buprenorphine (0.25 mg:2 mg for days1 to 3 and 0.5 mg:4 mg for days 4 to 7) Cohort B: 1:1 ratio of Compound1: Buprenorphine (4 mg:4 mg for days 1 to 3 and 8 mg:8 mg for days 4 to7

Visual analog scales (VAS) were used to assess drug liking and othersubjective drug effects. Subjects on active drug at the 1:8 ratioexperienced greater subjective experiences of “Feeling High” (Table D)and “Feeling Sedated” (Table E) compared to the 1:1 ratio. The VASresults are reported as predose and postdose scores showing themagnitude of difference in the subjective experiences. For example, onDay 7, the predose Cohort A VAS score for “Feeling High” was 5.8 andpostdose score was 32.9, showing a difference of 27.1 score before andafter dosing. In case of Cohort B, the predosing VAS score was 14.5 andpostdosing was 19.6 showing only an increase of 5.1. The comparisonbetween the two cohorts shows that Cohort A experienced a significantincrease in “Feeling High” after the dosing compared to Cohort B.

TABLE D Visual analog scale (VAS) results for “feeling high” PlaceboCohort A (1:8) Cohort B (1:1) Timepoint (mean[SD]) (mean[SD]) (mean[SD])Day 1 Predose 18.0 (20.98)  8.6 (19.58)  9.1 (13.70) Postdose 48.0(32.04) 54.4 (36.63) 29.4 (30.87) Day 2 Predose 6.8 (4.65) 14.8 (16.97)22.5 (23.63) Postdose 9.0 (8.76) 39.3 (29.40) 31.5 (29.02) Day 3 Predose7.3 (2.63)  7.2 (11.35) 22.7 (27.21) Postdose 6.3 (8.66) 41.8 (30.31)35.5 (32.42) Day 4 Predose 6.3 (4.92) 10.2 (9.94)  17.5 (22.92) Postdose 7.8 (10.97) 57.1 (30.21) 19.1 (23.19) Day 5 Predose  7.3 (10.59) 6.3(4.52) 15.7 (20.68) Postdose 23.8 (33.05) 35.1 (34.95) 19.5 (27.58) Day6 Predose 22.8 (25.68) 4.6 (3.29) 15.5 (21.99) Postdose 29.3 (32.35)43.7 (30.21) 22.1 (30.36) Day 7 Predose 24.5 (26.85) 5.8 (5.37) 14.5(23.57) Postdose 9.0 (8.76) 32.9 (30.14) 19.6 (29.51)

TABLE E Visual analog scale (VAS) results for “feeling sedated” PlaceboCohort A (1:8) Cohort B (1:1) Timepoint (mean[SD]) (mean[SD]) (mean[SD])Day 1 Predose 5.3 (9.24) 17.5 (26.98) 3.0 (4.96) Postdose 36.5 (38.73)60.4 (28.73) 34.3 (31.51) Day 2 Predose 5.5 (6.61) 11.5 (12.80) 13.8(15.42) Postdose 6.3 (6.75) 48.9 (28.69) 37.8 (31.21) Day 3 Predose 5.5(5.32) 8.2 (8.64) 21.6 (27.76) Postdose 4.5 (3.87) 49.0 (32.63) 31.2(29.48) Day 4 Predose 5.8 (6.02) 12.2 (15.80) 22.4 (25.55) Postdose 2.8(2.22) 38.4 (34.01) 22.2 (24.54) Day 5 Predose 4.0 (3.56)  9.5 (13.69)13.9 (18.05) Postdose 30.0 (34.55) 37.0 (31.65) 20.2 (23.79) Day 6Predose  9.8 (14.93) 6.5 (5.68) 10.6 (14.65) Postdose 21.3 (25.62) 44.8(31.26) 19.5 (24.77) Day 7 Predose 10.8 (10.53) 17.0 (21.21)  9.7(12.91) Postdose 5.3 (3.77) 30.3 (25.12) 14.5 (24.22)

Bioanalytical method used for determining the C_(max) for Compound-1: Amethod was validated for measuring Compound-1 in human plasma (K2EDTA).Samples were analyzed using a 50 μL aliquot volume and aprotein-precipitation extraction procedure followed by liquidchromatography/tandem mass spectrometry (LC/MS/MS). Compound-1concentrations were calculated with a 1/x² linear regression over aconcentration range of 0.250 to 100 ng/mL using naltrexone-d3 as aninternal standard. Ten-fold dilution was successfully tested at 400ng/mL for both analytes. The API 5000 was operated in the SelectedReaction Monitoring (SRM) mode under optimized conditions for detectionof Compound-1, naltrexone-d3 positive ions formed by electrosprayionization.

Bioanalytical method used for determining the C_(max) for buprenorphine:A method was validated for measuring buprenorphine in human plasma(K2EDTA). Samples were analyzed using a 400 μL aliquot volume and asolid-phase extraction procedure followed by liquidchromatography/tandem mass spectrometry (LC/MS/MS). Buprenorphineconcentrations were calculated with a 1/x² linear regression over aconcentration range of 0.250 to 100 ng/mL. The API 5000 was operated inthe Selected Reaction Monitoring (SRM) mode under optimized conditionsfor detection of buprenorphine and buprenorphine-d₄ positive ions formedby electrospray ionization.

The [³⁵S]GTPγS assay measures the functional properties of a compound byquantifying the level of G-protein activation following agonist bindingin studies using stably transfected cells, and is considered to be ameasure of the efficacy of a compound. Membranes from CHO (ChineseHamster Ovary) cells that stably expressed the cloned human g opioidreceptor were used in the experiments. In a final volume of 0.5 mL, 12different concentrations of Compound-1 were incubated with 7.5 μg of CHOcell membranes that stably expressed the human μ opioid receptor. Theassay buffer consisted of 50 mM Tris-HCl, pH 7.4, 3 mM MgCl₂, 0.2 mMEGTA, 3 04 GDP, and 100 mM NaCl. The final concentration of [³⁵S]GTPγSwas 0.080 nM. Nonspecific binding was measured by inclusion of 10 μMGTPγS. Binding was initiated by the addition of the membranes. After anincubation of 60 min at 30° C., the samples were filtered throughSchleicher & Schuell No. 32 glass fiber filters. The filters were washedthree times with cold 50 mM Tris-HCl, pH 7.5, and were counted in 2 mLof Ecoscint scintillation fluid. Data are the mean Emax and EC₅₀values±S.E.M. For calculation of the Emax values, the basal [35S]GTPγSbinding was set at 0%, and the 100% [³⁵S]GTPγS binding level was set atthe maximum binding achieved with DAMGO.

Example 2

Experiments were conducted in rats to assess the ability of opioidantagonists to modulate buprenorphine-induced dopamine efflux in theNucleus Accumbens shell (NAc-sh) region of the mesolimbic region of thebrain. Male rats weighing 300-400 grams were used for all studies. Tomeasure the efflux of dopamine in the NAc-sh an in vivo microdialysismethod was utilized in free-moving rats. This method allows the samplingof extracellular cerebrospinal fluid (CSF) from specific brain regionsof interest and measurement of neurotransmitter concentrations followingthe analysis of sampled dialysate with HPLC-EC.

Each rat underwent surgical implantation of microdialysis guide cannula(CMA 12, CMA Microdialysis) to facilitate the insertion of themicrodialysis probe later on. Rats were anesthetized with a mixture ofketamine/xylazine (80/6 mg/kg IP) and placed in a stereotaxic apparatus.Using bregma and skull as reference points, final coordinates weredetermined by The Rat Brain in Stereotaxic Coordinates (Paxinos andWatson, 2006) for the nucleus accumbens shell (+1.7 A/P, +−0.80 M/L,−7.8 D/V) and the guide cannula were lowered vertically into position(D/V=−5.8 from the skull) and fixed to the skull with glass-ionomerdental acrylic. Guide cannula were capped with dummy probes untilmicrodialysis probe insertion. On the day prior to experimentation (3-4days post surgery), animals were weighed to determine appropriate dosefor test articles. A microdialysis probe (CMA 12, 2 mm membrane, CMAmicrodialysis) was then inserted through the guide cannula.Microdialysis probes were connected to a tether system allowing freemovement and sterile artificial CSF (aCSF) (CMA microdialysis) waspumped via microsyringe pumps at a rate of 0.25 μL/min through the probeovernight for approximately 16 hours prior to experimentation. On theday following probe insertion, sterile aCSF perfusion was increased to2.0 μl/min and a pre-baseline equilibration period was established forat least 1.5 hours prior to initiating continuous collection of CSF.After the equilibration period a baseline neurotransmitter levels weredetermined for each animal over 1.75 hours. Following this baselineperiod, antagonist plus buprenonorphine (0.1 mg/kg, SC) wereadministered and continuous sampling of the microdialysate conducted foran additional 4.25 hours. While continuously collected, the CSF wasautomatically fractioned into 15 minute periods using a chilledmicrofraction collector for the entire 6.0 hours collection period (1.75baseline phase and 4.25 hour treatment phase). Each sample was analyzedvia HPLC-EC to determine neurotransmitter concentration of dopaminebased upon a six-point standard curve. The average dopamine per sampleover the 4.25 treatment phase was used in all comparisons amongtreatment groups.

In rats buprenorphrine resulted in dose dependent increases in NAc-shdopamine efflux between doses of 0.01 and 1 mg per kg (FIGS. 1 and 2).At doses of 0.1 and 1.0 mg per kg behavioral effects of buprenorphinewere observed, including initial sedation followed by hyperactivity.Consequently all additional experiments with μ opioid antagonist used adose of 0.1 mg per kg of buprenorphine since it represented the lowestdose associated with clear behavioral effects. As shown in FIG. 3 eachof the four antagonists evaluated resulted in linear dose-dependentdecreases in NAc-sh dopamine efflux. However, the range in apparentpotencies was considerable. Based on the AAnAI concept, this result wasexpected since neither differences in potency at the μ opioid receptoror in the pharmacokinetic properties of the antagonists is taken intoaccount.

TABLE F C_(max) values for Compound-1, Compound-10, naltrexone andnalmefene with Buprenorphine (0.1 mg/kg) Dose of Antagonist mg per kgAntagonist 0.03 0.1 0.3 1.0 Compound-1 — — 11.8 75.5 Compound-10 2.2418.1 29.5 — Naltrexone — 19.27 76.9 169 Nalmefene — 14.13 25.6 162

Example 3

The AAnAI concept was applied to the study results obtained where NAc-shdopamine efflux was attenuated with increasing doses of the fourμ-opioid receptor antagonist antagonists. Due to the inherent minorstress associated with PK sampling, and the sensitivity of neuralchemistry to this stress, different groups of animals were required toestablish circulating concentrations of buprenorphine and theantagonists at each dose level evaluated. Male rats weighing between300-400 grams, the same weight range used in the microdialysis studies,were used for these PK experiments. Since all animals received a fixeddose of buprenorphine, a commercial formulation of buprenorphine(Buprenex (Reckitt Benckiser)) was diluted to 0.1 mg/ml with sterilesaline and then used as the vehicle for the required doses of Compound1, Compound-10, naltrexone and nalmefene. This approached ensured thatat each dose of the antagonist studied the concomitant dose ofbuprenorphrine would be 0.1 mg per kg. All injections were made by thesubcutaneous route at the doses indicated in Table G. Sterile solutionsof the test formulations (combination of antagonist with 0.1 mg/kgbuprenorphine) were given subcutaneously (designated as time 0). Sampleof blood were collected at 5, 15, 30, 60 and 120 minutes post dosing.For each blood sampling time point, rats were lightly anesthetized using(3%) isoflourane anesthesia and approximately 200 μl of blood waswithdrawn from the lateral tail vein using a 27.5 gauge needle andplaced into chilled K2 EDTA tubes. The collection tubes were inverted10-15 times and then held on ice prior to centrifugation. Plasma wasobtained by centrifuging samples for 2 minutes at 14,000×g (11,500 RPMusing Eppendorf 5417R centrifuge rotor) at 4° C. The harvested samplesof plasma were frozen at −80° C. until assayed for buprenorphine and theantagonists (Compound 1, Compound 10, naltrexone or nalmefene). TheC_(max) values for each antagonist at the doses evaluated are shown inTable F. These values were used to calculate the AAnAI index associatedwith reductions in NAc-sh DA with increasing administered doses of theantagonist, taking into account differences in potency and PK propertiesamong these compounds. As can be seen from FIG. 3, the variability inthe NAc-sh dopamine shown in Table E across the antagonist wasessentially eliminated for Compound I, Compound-10 and naltrexone bytaking into account the in vitro potency and the C_(max) achieved.Nalmefene did appear more potent in attenuating buprenorphine-inducedNAc-sh dopamine efflux, indicating that in rats other factors mayinfluence the NAc-sh dopamine response to nalmefene.

TABLE G Calculated AAnAI values for varying doses of Compound-1,Compound-10, naltrexone and nalmefene with Buprenorphine (0.1 mg/kg)Antagonist Dose of Antagonist mg per kg Antagonist IC₅₀ (nM) 0.03 0.10.3 1.0 Compound-1 0.9 — — 2.04 0.33 Compound-10 0.23 2.58 0.92 0.2 —Naltrexone 4.8 — 5.79 1.47 0.67 Nalmefene 13 — 3.83 2.02 0.31

Example 4

The desired range of the AAnAI to achieve a clinical anti-depressiveeffect is between values of about 0.5 and 5, and preferably about 0.7and 2.2. These ranges take into account the inherent variability inassay methods used to experimentally determine values for the EC₅₀ ofbuprenorphine and its concentration in plasma, and the IC₅₀ of opioidantagonists and their concentrations in plasma for both non-clinical andclinical studies. As cited in Example 1, with plasma C_(max) values forbuprenorphine and Compound 1 resulting in AAnAI values of greater than5, patients reported experiencing greater subjective feelings of highand sedation; undesirable traits for a buprenorphine and opioidantagonist combination intended for the treatment of depression. In the“forced swim test” (FST) rats are placed in a tank of water, from whichthey cannot escape, on two successive days; 15 minutes on the first dayand 5 minutes on the second day. While in the water they will swim,attempt to climb the container wall or become “immobile” floating in thewater. The total time rats are immobility increases between the firstand second day. Drugs that have antidepressant effects in humans reduceimmobility time on day 2 and this model is frequently used to evaluatepotential anti-depressive like activity of drugs. Strain of rat can alsoaffect total immobility time, with the Wistar-Kyoto (WKY) strain showinghigh immobility times. The WKY rat is spontaneously hypertensive anddisplays hormonal and depressive-like behavioral abnormalities. Toexplore the lower end of the range of the AAnAI, an experiment wasconducted using three groups of rats in the FST paradigm. Rats receivedthree separate subcutaneous injections of either vehicle alone or acombination of buprenorphine (0.1 mg/kg) and Compound-1 (0.3 or 3.0mg/kg) at 1, 19, and 23 h after the first exposure to the swim tanks. At24 h after the first swim, rats were retested for 5 minutes. Videos werescored manually for immobility time (in seconds) using a manual stopwatch in 60 second intervals by a rater blinded to the treatment groups.A rat was judged to be immobile if it was making only movementsnecessary to keep its head above water. Results for this study are shownin FIG. 5. Immobility time was significantly lower (p<0.05) in ratsgiven the combination of buprenorphine and Compound 1 at 0.3 mg/kg,indicating an anti-depressive like action. An AAnAI value ofapproximately 2 was associated with this dose combination ofbuprenorphine and Compound 1. The anti-depressive like effect of thecombination was lost when the dose of antagonist was raised to 3.0 mg/kgwhen an AAnAI of less than 0.3 was achieved. These data, along with theclinical data shown in Example 1 illustrate the importance of both theupper and lower boundaries of the AAnAI in order to achieve ananti-depressant activity without undesired side effects. FIGS. 6 and 7,show the complete attenuation of buprenorphine effects at the highestdose of Compound 1 for NAc-sh dopamine and 5-HIAA. These data furtherillustrate that at the desirable dose combination effects ofbuprenorphine are being modulated, but not eliminated, by Compound 1.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A composition comprising buprenorphine and a μ opioid receptorantagonist, wherein the composition is characterized by an AgonistAntagonist Activity Index (AAnAI) of between about 0.7 and about 2.2;wherein;${AAnAI} = \frac{\left\lbrack {C_{\max {({BUP})}}/{EC}_{50}} \right\rbrack}{\left\lbrack {C_{\max {({ANTAGONIST})}}/{IC}_{50}} \right\rbrack}$wherein, EC₅₀ represents the half maximal effective serum concentrationof buprenorphine, expressed as nM; IC₅₀ represents the half maximalinhibitory concentration of the μ opioid antagonist in humans, expressedas nM; C_(max(BUP)) represents the peak serum or plasma concentration ofbuprenorphine and/or a μ opioid receptor agonist metabolite ofbuprenorphine, expressed as nM; and C_(max(ANTAGONIST)) represents thepeak serum concentration of the μ opioid antagonist and/or a μ opioidreceptor antagonist metabolite of said μ opioid antagonist, expressed asnM.
 2. The composition according to claim 1, wherein said AAnAI isbetween about 0.8 and about 2.1, or between about 0.9 and about 2.0, orbetween about 1.0 and about 1.8, or between about 1.1 and about 1.6, orbetween about 1.2 and about 1.4.
 3. The composition according to claim1, wherein said antagonist is a compound of Formula I:

or a pharmaceutically acceptable salt, ester or prodrug thereof wherein;s is 0, 1 or 2; t is 0, 1, 2, 3, 4, 5, 6, or 7; X is S or O; R₁ isselected from aliphatic, substituted aliphatic, aryl, substituted aryl,heterocyclyl or substituted heterocyclyl; each R₂, R₃, R₄, R₅, R₆, R₇and R₈ is independently selected from absent, hydrogen, halogen, —OR₂₀,—SR₂₀, —NR₂₀R₂₁, —C(O)R₂₀, —C(O)OR₂₀, —C(O)NR₂OR₂₁, —N(R₂₀)C(O)R₂₁,—CF₃, —CN, —NO₂, —N₃, acyl, alkoxy, substituted alkoxy, alkylamino,substituted alkylamino, dialkylamino, substituted dialkylamino,substituted or unsubstituted alkylthio, substituted or unsubstitutedalkylsulfonyl, optionally substituted aliphatic, optionally substitutedaryl, heterocyclyl or substituted heterocyclyl; each R₉ and R₁₀ isselected from hydrogen, aliphatic, substituted aliphatic, aryl,substituted aryl, heterocyclyl or substituted heterocyclyl;alternatively, two of R₂, R₃, R₄, R₅, R₆, R₇ and R₈ together with theatoms they are attached to form an optionally substituted ring;alternatively R₂ and R₃ together with the carbon they are attached toform a C═X group; wherein each R₂₀ and R₂₁ is independently selectedfrom absent, hydrogen, halogen, —OH, —SH, —NH₂, —CF₃, —CN, —NO₂, —N₃,—C(O)OH, —C(O)NH₂, acyl, alkoxy, substituted alkoxy, alkylamino,substituted alkylamino, dialkylamino, substituted dialkylamino,substituted or unsubstituted alkylthio, substituted or unsubstitutedalkylsulfonyl, aliphatic, substituted aliphatic, aryl or substitutedaryl; and alternatively R₉ and R₁₀ together with the atom they areattached to form an optionally substituted ring; alternatively two R₅groups, or an R₅ and an R₆ group, together with the carbon they areattached to form a C═X group.
 4. The composition according to claim 3,wherein said antagonist is a compound of Formula II:

or a pharmaceutically acceptable salt, ester or prodrug thereof wherein;R₁ is —(CH₂)_(n)-c-C₃H₅, —(CH₂)_(n)-c-C₄H₇, —(CH₂)_(n)-c-C₅H₉,—(CH₂)_(n)—CH═CH₂ or —(CH₂)_(n)—CH═C(CH₃)₂ wherein n and m areindependently 0, 1, 2 or 3; R₆ and R₇ are independently H, —OH ortogether R₆ and R₇ form an —O- or —S-group; and R₅ and R₁₁ areindependently H, —OH, OCH₃ or together R₅ and R₁ form a ═O or ═CH₂group.
 5. The composition according to claim 4, wherein said antagonistis selected from:


6. A composition comprising buprenorphine and a compound of Formula I:

or a pharmaceutically acceptable salt, ester or prodrug thereof wherein;s is 0, 1 or 2; t is 0, 1, 2, 3, 4, 5, 6, or 7; X is S or O; R₁ isselected from aliphatic, substituted aliphatic, aryl, substituted aryl,heterocyclyl or substituted heterocyclyl; each R₂, R₃, R₄, R₅, R₆, R₇and R₈ is independently selected from absent, hydrogen, halogen, —OR₂₀,—SR₂₀, —NR₂₀R₂₁, —C(O)R₂₀, —C(O)OR₂₀, —C(O)NR₂₀R₂₁, —N(R₂₀)C(O)R₂₁,—CF₃, —CN, —NO₂, —N₃, acyl, alkoxy, substituted alkoxy, alkylamino,substituted alkylamino, dialkylamino, substituted dialkylamino,substituted or unsubstituted alkylthio, substituted or unsubstitutedalkylsulfonyl, optionally substituted aliphatic, optionally substitutedaryl, heterocyclyl or substituted heterocyclyl; Each R₉ and R₁₀ isselected from hydrogen, aliphatic, substituted aliphatic, aryl,substituted aryl, heterocyclyl or substituted heterocyclyl;alternatively, two of R₂, R₃, R₄, R₅, R₆, R₇ and R₈ together with theatoms they are attached to form an optionally substituted ring;alternatively R₂ and R₃ together with the carbon they are attached toform a C═X group; wherein each R₂₀ and R₂₁ is independently selectedfrom absent, hydrogen, halogen, —OH, —SH, —NH₂, —CF₃, —CN, —NO₂, —N₃,—C(O)OH, —C(O)NH₂, acyl, alkoxy, substituted alkoxy, alkylamino,substituted alkylamino, dialkylamino, substituted dialkylamino,substituted or unsubstituted alkylthio, substituted or unsubstitutedalkylsulfonyl, aliphatic, substituted aliphatic, aryl or substitutedaryl; and alternatively R₉ and R₁₀ together with the atom they areattached to form an optionally substituted ring; alternatively two R₅groups, or an R₅ and an R₆ group, together with the carbon they areattached to form a C═X group.
 7. The composition according to claim 6,wherein said compound of Formula I is a compound of Formula II:

or a pharmaceutically acceptable salt, ester or prodrug thereof wherein;R₁ is —(CH₂)_(n)-c-C₃H₅, —(CH₂)_(n)-c-C₄H₇, —(CH₂)_(n)-c-C₅H₉,—(CH₂)_(n)—CH═CH₂ or —(CH₂)_(n)—CH═C(CH₃)₂ wherein n and m areindependently 0, 1, 2 or 3; R₆ and R₇ are independently H, —OH ortogether R₆ and R₇ form an —O- or —S-group; and R₅ and R₁₁ areindependently H, —OH, OCH₃ or together R₅ and R₁ form a ═O or ═CH₂group.
 8. The composition according to claim 6, wherein said compound ofFormula I is selected from:


9. A composition according to claim 3, wherein said compound of FormulaI is:

or its pharmaceutically acceptable salt, ester or prodrug.
 10. A methodof treating a depressive disorder comprising administering a compositionaccording to claim 1 to a subject in need thereof.
 11. The methodaccording to claim 10, wherein said depressive disorder is selected frommajor depressive disorder, chronic depression, severe unipolar recurrentmajor depressive episodes, dysthymic disorder, depressive neurosis andneurotic depression, melancholic depression, atypical depression,reactive depression, treatment resistant depression, seasonal affectivedisorder and pediatric depression; premenstrual syndrome, premenstrualdysphoric disorder, hot flashes, bipolar disorders or manic depression,bipolar I disorder, bipolar II disorder and cyclothymic disorder. 12.The method according to claim 10, wherein said depressive disorder ismajor depressive disorder.
 13. The method according to claim 11, whereinsaid major depressive disorder is resistant to two or moreantidepressants.
 14. The method according to claim 12, wherein theantidepressants are selected from the group comprising selectiveserotonin reuptake inhibitors (SSRIs), Serotonin-norepinephrine reuptakeinhibitors (SNRIs), Monoamine oxidase inhibitors (MAOIs) and Tricyclicantidepressants.
 15. The method according to claim 10, wherein saiddepressive disorder is treatment resistant depression.
 16. The methodaccording to claim 10, wherein composition is administered orally orsublingually.
 17. The method according to claim 10, wherein said subjectexhibits one or more depressive symptoms selected from irritability,feelings of hopelessness and helplessness, inability to concentrate,sadness, insomnia, appetite loss, lack of interest in life's activities,thoughts of suicide, dizziness, nausea, vomiting, hyperhidrosis,menorrhagia, pain in extremity, constipation, sedation, fatigue, feelingabnormal, flushing and somnolence.
 18. The method according to claim 10,wherein said μ opioid antagonist is:

or a salt, ester or prodrug thereof.
 19. A composition comprising about1 mg to about 100 mg of buprenorphine and about 0.25 to about 100 mg ofa compound of Formula I.
 20. The composition of claim 19 comprisingabout 2 mg to about 50 mg of buprenorphine.
 21. The composition of claim19 comprising about 3 to about 25 mg of buprenorphine.
 22. Thecomposition of claim 19 comprising about 3 to about 10 mg ofbuprenorphine.
 23. The composition according to claim 20 comprisingabout 0.25 to about 50 mg of a compound of Formula I.
 24. Thecomposition according to claim 19 comprising about 0.5 to about 25 mg ofa compound of Formula I.
 25. The composition according to claim 19comprising about 1.0 to about 20 mg of a compound of Formula I.
 26. Thecomposition according to claim 19 comprising about 2.0 to about 10 mg ofa compound of Formula I.
 27. The composition according to claim 19wherein said compound of Formula I is a compound of Formula II.
 28. Thecomposition according to claim 19 wherein said compound of Formula I isselected from:


29. The composition according to claim 19, wherein said compound ofFormula I is:

or a pharmaceutically acceptable salt, ester or prodrug thereof.
 30. Amethod of treating a depressive disorder selected from major depressivedisorder, chronic depression, severe unipolar recurrent major depressiveepisodes, dysthymic disorder, depressive neurosis and neuroticdepression, melancholic depression, atypical depression, reactivedepression, treatment resistant depression, seasonal affective disorderand pediatric depression; premenstrual syndrome, premenstrual dysphoricdisorder, hot flashes, bipolar disorders or manic depression, bipolar Idisorder, bipolar II disorder and cyclothymic disorder comprising thestep of administering a composition according to claim 1 to a subject inneed thereof.
 31. A method of treating a disease or disorder selectedfrom obsessive compulsive disorder, bulimia nervosa, panic disorder,posttraumatic stress disorder (PTSD), premenstrual dysphoric disorder(PMDD), social anxiety disorder and generalized anxiety disorder(GAD).comprising the step of administering a composition according toclaim 1 to a subject in need thereof.
 32. A composition according toclaim 1, wherein said composition has an AAnAI of about 1.3.